1. Field of the Invention
This invention relates to a cap for a writing instrument, and particularly to a cap of a double-tube construction in which an air communicating portion is secured in an inner peripheral surface of an outer tube having front and rear open portions, a closed-end tubular inner tube is held coaxially within the outer tube. Thus, a permeable cap provided with a suffocation preventive construction in which even if a curious child or the like should accidentally swallow and lodge the cap in its throat or bronchus, a sufficient flow of air is provided to avoid suffocation.
2. Description of Prior Art
In the past, a cap for a writing instrument of a double construction has been known which comprises an outer tube having front and rear open portion and a closed-end tubular inner tube which is held coaxially within the outer tube such that an air communicating portion is provided in an inner peripheral surface of the outer tube and which is in contact with an outer peripheral surface of a front-portion of an axial tube from which a pen body projects when the cap mounted to the axial tube to seal the pen body. The cap includes a tapered portion that guides the pen body into the inner tube during the mounting process to the axial tube (disclosed, for example, in Japanese Utility Model Laid-Open Nos. Hei 2-58981 and 4-117790).
For example, the conventional cap disclosed in the aforementioned Japanese Utility Model Laid-Open No. Hei 4-117790 is constructed such that an outer tube and an inner tube are integrally connected at a bridge portion so that the inner tube is held coaxially within the outer tube, a front surface of the bridge portion facing a front-end opening side of the outer tube comprises a taper portion that is enlarged and inclined from a front-end opening of the inner tube toward the front-end opening side of the outer tube. A pen body is guided into the inner tube by the tapered portion when the cap is mounted to an axial tube. The bridge portion provided with the taper portion is peripherally provided with several vent holes extending through the air communicating portion from the taper portion to provide a permeable cap in which the rear-end opening side and the front-end opening side of the outer tube are in communication, Thus, even if a child or the like should accidentally swallow the cap and lodge the same in its throat or bronchus, suffocation can be avoided by communication of air from the rear-end opening side to the front-end opening side or from the front-end opening side to the rear-end opening side of the outer tube by providing air through the air communicating portion and several vent holes provided in the bridge portion.
The taper portion of the bridge portion that integrally connects and holds the outer tube and the inner tube guides and leads the pen body into the inner tube, as mentioned above, while contacting the pen body to the axial tube. Therefore, during a guiding of the pen body into the inner tube, ink tends to be adhere to the taper portion, such adhesion being unavoidable. Accordingly, in the past, the ink adhered to the taper portion is likely to flow into the vent holes of the bridge portion from the taper portion toward the air communicating portion and becomes solidified therein to close the vent holes. That is, permeability of the cap can be impeded.